Wednesday, April 2, 2008

Highly oriented monolayer graphite formation on Pt(111) by a supersonic methane beam

Highly oriented monolayer graphite formation on Pt(111) by a supersonic methane beam.

Hirokazu Ueta, Morihiko Saida, Chikara Nakai, Yoichi Yamada, Masahiro Sasaki, and Shigehiko Yamamoto

Surface Science, 2004, 560(1-3), 183-190.

Ok, so really I just wanted to post this because the authors use a supersonic methane beam. I mean, are you kidding me? Supersonic? Methane? Beam? I want one, even if all it does is leave a thin layer of graphite upon mine enemies.

So let's cut to the chase- the background portion of this paper mentions that "single layer graphite" is made by thermal decomposition of hydrocarbons on a metal surface (usually using CVD)- I posted on this before, and there are supposedly papers going back to 1975 that have done similar things. This is how one makes the fancy graphite used for "Scotch tape" graphene exfoliation, and closely related techniques are used to make carbon nanotubes. The authors of this paper mention that the graphene layers made by this method are often quite heterogeneous and that other carbon structures are present, making characterization difficult. Their solution is to use kinetic instead of thermal energy to convert hydrocarbons (methane) into graphene.

So, a quick word on their setup: they shoot methane onto a substrate that's connected to a mass spec, then take the substrate out and take some STM images. Here's their schematic of the device:

So now you can go home and build one yourself. After blasting their platinum substrate with methane, they look at it with STM (using the local tunneling barrier height technique, LBH, which I'll skip for now) and, as expected, find a Moire pattern, suggesting few- or single-layer graphene. They make two major finds:

First, their domain size is much larger than in contemporary (2004) thermal graphitization techniques, meaning they get a more homogeneous film. For this to happen, the graphene layers must be reasonably mobile on the surface. Graphene made with higher kinetic energy methane was the most homogeneous.

Second, they imply that their graphene layers actually grow over the step (like a blanket on a pillow; a similar effect was found in the previously mentioned post) instead of stopping and starting on steps.

What does these two things have in common? The authors suggest that the mobility of the graphene layers and their independence from surface features mean that the film doesn't interact very much with the metal surface, both during graphitization and afterwards. This is a good thing, since surface defects won't be translated into the final product, and the smaller interaction may also give different electronic (or catalytic) properties. The authors finish with a discussion of how the kinetic energy they use effects the film, and also make a comment about how the graphene must be distorted to give a lower-energy conformation (this seems a bit dated), but we'll wrap it up knowing that our graphene just has a lower interaction with the metal surface.

All in all, the graphene layers made here are not very uniform (compared to current 2008 techniques) and probably won't be used for industrial purposes. It's still a nice paper that uses a technique equal in coolness to sharks with laser beams on their heads.

UETA, H. (2004). Highly oriented monolayer graphite formation on Pt(111) by a supersonic methane beam. Surface Science, 560(1-3), 183-190. DOI: 10.1016/j.susc.2004.04.039